In IEEE (institute of electrical and electronics engineers) 802.16m system for example of AAI (advance air interface frame) system, a frame consists of a plurality of subframes and each of the subframes consists of a plurality of subcarriers on a frequency axis and a plurality of OFDM symbols on a time axis. Some of a plurality of subframes included in one frame are used to transmit uplink (UL) data and the rest are used to transmit DL data. In the following description, a frame structure of IEEE 802.16m system is schematically explained.
FIG. 1 is a diagram of a basic frame structure in IEEE (institute of electrical and electronics engineers) 802.16m system.
Referring to FIG. 1, each 20 ms superframe is divided into 4 5 ms frames in equal size. The 5 ms frame has a channel bandwidth amounting to one of 5 MHz, 10 MHz and 20 MHz. and, each 5 ms radio frame may consist of 8 subframes in accordance with the channel bandwidth.
One subframe may be allocated to downlink (DL) transmission or uplink (UL) transmission. One subframe may consist of OFDMA (orthogonal frequency division multiple access) symbols of which number varies in accordance with a channel bandwidth. A 1st type subframe may be defined as the subframe consisting of 6 OFDMA symbols, a 2nd type subframe may be defined as the subframe consisting of 7 OFDMA symbols, and a 3rd type subframe may be defined as the subframe consisting of 5 OFDMA symbols.
The hybrid automatic retransmission request (hereinafter abbreviated HARQ) means an advanced automatic retransmission request scheme of performing decoding in a manner of combining originally transmitted information and retransmitted information together to decrease a count of transmissions due to error occurrence in initial data transmission. This hybrid automatic retransmission request (HARQ) scheme corresponds to a technique used not only for IEEE 802.16m system but also for other mobile communication systems. For the HARQ feedback scheme, IEEE 802.16m system has only proposed a case that one frame consists of 8 subframes.
However, in case that one frame consists of 5, 6 or 7 subframes in IEEE 802.16m system, it is impossible to apply the related art HARQ feedback scheme. Therefore, the demand for a method of HARQ feedback for such a case is rising.